Add jsx-a11y eslint plugin (#7434)

* add matrix-org a11y eslint plgin

Signed-off-by: Kerry Archibald <kerrya@element.io>

* add eslint a11y, enable and fix anchor-has-content rule

Signed-off-by: Kerry Archibald <kerrya@element.io>

* enable and fix jsx-a11y/no-redundant-roles

Signed-off-by: Kerry Archibald <kerrya@element.io>

* remove debug

Signed-off-by: Kerry Archibald <kerrya@element.io>

* i18n

Signed-off-by: Kerry Archibald <kerrya@element.io>

* use jsx-a11y via matrix-org-eslint

Signed-off-by: Kerry Archibald <kerrya@element.io>

src/components/structures/ScrollPanel.tsx

@@ -958,7 +958,7 @@ export default class ScrollPanel extends React.Component<IProps> {
             >
                 { this.props.fixedChildren }
                 <div className="mx_RoomView_messageListWrapper">
-                    <ol ref={this.itemlist} className="mx_RoomView_MessageList" aria-live="polite" role="list">
+                    <ol ref={this.itemlist} className="mx_RoomView_MessageList" aria-live="polite">
                         { this.props.children }
                     </ol>
                 </div>